Look I I know the whole Amulet thing is for kids, but I had been thinking, where the hell is the US gov? It might be true that Silas Charnon is the only human from Alledia and stayed in an area of the US, while his kids and later grandchildren like Navin and Emily are don't have any knowledge like Silas have. Yet I have been thinking, if the US Gov find something unnatural from their satellites and when they found out that Silas is not from around any places on Earth will question him who and where is he from. I believed Silas will warn the US gov about the Shadows' dangerous exsistance, his homeworld and what the stonekeepersare to have his freedom and later live peacefully till old age. The gov will let him live and will use their tech to monitor the whole situation on Alledia by sending stealth satellites to the world's space. If the whole thing goes out of control while Emily and her family are on the planet, the US might send in agents from the CIA and operators from Special Forces/Special Operations Forces to try to destroy the Shadows by using some anti-shadow weapon(possibly Silas' design) and regular weapons to stop the elves' military forces from Gulfen. Moreover I think they won't like the stonekeepers, because to me they are the Amulet version of the Jedi from Star Wars, but will work together to take care of Alledia's threats. Later the Americans might find a way to control then lock up Ikol and stop him from destroying Alledia. After those threats are gone, they might make a short truce with the Alledia nations and more importantly sharing both sides' skills to tech to strengthen both sides easily. Yes the Shadows are a dying race but invading another planet is just going to spell faster death when the US gov knows this.
Just want to say, saving the world(not just Alledia) isn't by some little girl using stones, but by a government to possibly superpowers to deal with the threats that no mortal can stop. Last but not least, the Alledia nations don't seem to have the power to use nuclear weapons or some weapons of mass destruction(WMD) like our nations on Earth, maybe the stonekeepers are their "WMDs" so their tech in some conditions don't make scenes. Like mechs or airships, modern fighter jets and battle tanks are going to blow them the pieces from many km away. Other than that, soldiers using firearms than swords because guns can quickly kill enemies(even stonekeepers).
I hope Kazu can think about it.